The present invention relates to an impregnated cathode and an electron tube, especially a display tube and a pick up tube, using said impregnated cathode, and further to a cathode having a low work function mono-layer required for a particular low temperature operation on a cathode surface and an electron tube using said cathode.
The impregnated cathode formerly used for a low temperature operation is, as indicated in the Japanese Patent Application Laid Open No. 154131/1983, characterized in that it has a constitution of a porous base body consisting of W and Sc.sub.2 O.sub.3 impregnated with electron emissive materials; also it has a mono-layer consisting of Ba, Sc, and O on the cathode surface; and it forms a low work function surface. However, this mono-layer is defective in the following respects that: it is unstable against thermal shock or ion bombardment; it is short in life because of its non-uniform distribution, and also its electron emissive property deteriorates at a low electric field.